java inheritance help

[Borkil]

Hi I'm making a simple game in Java but I'm a little confused on why I'm getting a null exception in this function on "drawPile". I think I'm accessing a different drawPile in the child class.

	public GamePiece drawPiece(){
		Random rand = new Random();
		[b]System.out.println(this.drawPile.size()); //EXCEPTION!![/b]
		int randInt = rand.nextInt(this.drawPile.size());
		System.out.println("RANDOM INT: " + randInt);
		GamePiece drawnPiece = this.drawPile.get(randInt);
		this.drawPile.remove(randInt);
		return drawnPiece;
	}

This is called from a subclass Player in the function

	public void playerTurn(){
		currentPiece = this.drawPiece();
	}

REST OF CODE

public class Main {
	
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Game game = new Game();
		game.newGame();

	}
}

Game class.

import java.util.*;


public class Game {
	private GameBoard gameBoard; //the gameboard
	private HashMap<Integer, Player> players; //holds the player class
	private HashMap<Character, Integer> pieces; //holds the piece types and how many of each.
	private ScoreBoard scoreBoard; //the scoreboard
	private ArrayList<GamePiece> drawPile; //the pile of pieces that players draw from. game ends when empty
	private int playerCount; //# of players
	
	public void newGame(){

		this.gameBoard = new GameBoard();
		
		this.generatePlayers();
		this.generateDrawPile();
		this.drawPile.remove(drawPile.size() - 1);
		this.printDrawPile();
		System.out.println("***********NEW GAME**************");
		this.playGame();
	}
	
	public Game(){
	}
	
	public GamePiece drawPiece(){
		Random rand = new Random();
		System.out.println(this.drawPile.size());
		int randInt = rand.nextInt(this.drawPile.size());
		System.out.println("RANDOM INT: " + randInt);
		GamePiece drawnPiece = this.drawPile.get(randInt);
		this.drawPile.remove(randInt);
		return drawnPiece;
	}
	
	public static int getINTInput(String inst){
		@SuppressWarnings("resource")
		Scanner input = new Scanner(System.in);
		while(!input.hasNextInt()){
			System.out.println("Invalid input");
			System.out.println(inst);
			input.next();
		}
		return input.nextInt();
	}
	
	private void generateDrawPile(){
		this.drawPile = new ArrayList<GamePiece>();
		this.pieces = new HashMap<Character, Integer>();
		

		this.pieces.put('A', 2);
		this.pieces.put('B', 4);

		for(char key : this.pieces.keySet()){
			//System.out.println(key + " " + pieces.get(key));
			for(int i = 0; i < pieces.get(key); i++){
				this.drawPile.add(new GamePiece(key));
			}
		}
	}
	
	private void generatePlayers(){
		this.players = new HashMap<Integer, Player>();
		
		do{
			System.out.println("Input the number of players (2-5)");
			this.playerCount = Game.getINTInput("Input the number of players (2-5)");
			if (this.playerCount > 5 || this.playerCount < 2){
				System.out.println("Invalid input");
			}
		}while(this.playerCount > 5 || this.playerCount < 2);
		
		for(int i = 1; i <= this.playerCount; i++){
			this.players.put(i, new Player("Player" + Integer.toString(i)));
			this.players.get(i).printPlayerInfo();
		}
		
		
	}
	
	
	private void playGame(){
		int currentPlayer = 1;
		while(!this.drawPile.isEmpty()){
			this.players.get(currentPlayer).playerTurn();
			currentPlayer++;
			if(currentPlayer > this.playerCount){
				currentPlayer = 1;
			}
		}
	}
}

The Player class

public class Player extends Game {
	private String playerName;
	private int score;
	private GamePiece currentPiece;

	
	public Player(String name){
		this.playerName = name;
		this.score = 0;

	}

	public void playerTurn(){
		currentPiece = this.drawPiece();
	}
	

}

 

[Ken g6]

OK, the Game has-a Player. That's fine. But the Player is-a Game?

I think you're accessing the drawPile in the same class, but in a different instance.

Edit: If you want a further hint about what's going wrong, click here.

 

[Borkil]

lol well I was originally thinking that a game has players. Plus I wanted the players to have access to the drawPile. what's another way for the players to access the instance of the drawPile?

 

[Ken g6]

Perhaps each Player needs to know what (instance of a) Game they are playing?